1. Field of the Invention
The present invention relates to a valve timing adjusting mechanism for adjusting operation timing of intake and exhaust valves in an internal combustion engine.
2. Description of the Prior Art
Disclosed in Japanese Patent Publication No. 5(1993)-77842 is a valve timing adjusting mechanism of this kind which includes an internal gear formed with external helical teeth and mounted on either one of a crankshaft or a camshaft of the engine for rotation therewith, an external gear formed with internal helical teeth and assembled in surrounding relationship with the internal gear, the external gear being drivingly connected to the other one of the crankshaft and camshaft for rotation therewith, an intermediate gear set in meshing engagement with the external helical teeth of the internal gear and in meshing engagement with the internal helical teeth of the external gear, the intermediate gear set being disposed in an annular space between the internal and external gears to be moved in an axial direction for effecting relative rotation of the internal gear and the external gear thereby to change rotational phase between the crankshaft and the camshaft, and a hydraulic driving mechanism for effecting axial movement of the intermediate gear set.
In the valve timing adjusting mechanism described above, the intermediate gear set is composed of a primary gear formed with internal helical teeth in meshing engagement with the external helical teeth of the internal gear and external helical teeth in meshing engagement with the internal helical teeth of the external gear and an auxiliary gear formed with internal helical teeth in meshing engagement with the external helical teeth of the internal gear and external helical teeth in meshing engagement with the internal helical teeth of the external gear. The auxiliary gear is connected with the primary gear through a resilient member and loaded by the resilient member in an opposite direction relative to the primary gear to eliminate backlashes between the internal helical teeth of the auxiliary gear and the external helical teeth of the internal gear and between the external helical teeth of the auxiliary gear and the internal helical teeth of the external gear.
Since in the valve timing adjusting mechanism, the primary and auxiliary gears are loaded by the resilient member in the opposite direction to eliminate backlashes at the meshed portions of the component gears, it is needed to adjust the biasing force of the resilient member in accordance with torque fluctuation of the internal combustion engine. If the backlashes at the meshed portions may not be eliminated due to fatigue of the resilient member, there will occur problems such as the occurrence of gear noises, irregularity in operation of the intake and exhaust valves, etc. In addition, smooth axial movement of the intermediate gear set may not be effected due to frictional engagement forces caused by the resilient member.